The invention relates generally to bolts used to establish a channel through biological tissue and in particular, to a parenchymal bolt used to mount an instrument, such as a catheter, into the cranium for biomedical sensing or other purposes.
It has been the practice for many years to monitor the intracranial pressure of patients suffering from severe brain injuries. If the pressure rises above a critical level, pressure in the brain should be relieved by draining fluid from the affected ventricle. Several different structures have been proposed and adopted for this purpose. A catheter or the like is one such structure and may be inserted directly into the brain to accomplish these tasks. However, insertion of a catheter has been a difficult and risky procedure and requires a high level of skill. Chief among the risks is the possibility of bacterial infection. As a general rule, once the catheter has been inserted, it must be left in place for several days, and this makes the prevention of such infection both critically important and more difficult to accomplish.
Additionally, once positioned, it is important that the catheter remain in the selected position during the entire sensing period. Should the catheter be inadvertently withdrawn from the proper position in the brain, pressure changes or temperature changes may not be sensed. If the catheter were being used to drain excess fluid, this drainage procedure may be interrupted should the catheter be partially or fully withdrawn from the skull. Movement of the patient, either on his own initiative or by others, contact with the catheter outside the patient, and other forces may put strain on the catheter shaft tending to pull it from its established position in the skull of the patient. On the other hand, the catheter must be mounted so that it can be removed from the patient when needed. For example, removal may be required for recalibration of a sensor or for replacement of a sensor or drainage catheter.
A structure or arrangement of some type is required to stabilize the catheter so that it does not move during its period of operation in the brain. Because sensing may extend over many days, as mentioned above, the stabilizing arrangement must be robust and must provide a sterile communication with the patient to reduce the chances of infection.
In one prior approach, it is possible to insert such a catheter surgically through an opening in the skull, routing the catheter underneath the scalp against the surface of the skull for a significant distance from the opening in the skull and thence through an opening in the scalp to the outside world. This isolates the opening in the skull from contact with the environment outside the scalp and thereby reduces the opportunity for infectious agents to enter the opening in the skull. This approach has been favorably received and significantly reduces the risk of infection. However, insertion of the catheter by this method is time consuming and requires considerable surgical skill. Additionally, should the hospital staff need to remove the catheter for some reason, such as for recalibration, a substantial amount of time is required to extract it from the skull, pull it from the scalp tunnel, and reinstall it or a replacement catheter.
A parenchymal bolt structure, such as that shown in U.S. Pat. No. 4,903,707 to Knute entitled VENTRICULAR CATHETER ASSEMBLY is a different approach and has been found to be extremely useful in stabilizing a catheter used to sense pressure in the brain of a patient. An incision through the scalp to the skull is made and then a hole is bored through the skull. The bolt is then screwed into the bore hole and thereby establishes a sterile environment that reduces the chances for infection and firmly anchors the bolt in place in the skull. Through the bolt is a channel for receipt of an instrument such as a pressure sensing catheter. A threaded cap forces a clamp into contact with the catheter shaft as the cap is screwed onto the bolt body to hold the catheter in position in relation to the clamp, the bolt, and to the skull of the patient.
Requirements of such a bolt are that it be rapidly installable in the skull and that it work efficiently across a wide variety of skull types, including the much thinner pediatric skulls. The smaller pediatric skulls have much less thickness and in some cases do not provide the amount of material for the threads of the screw-type bolts to securely fasten to. It has been found that in such cases, some screw-type bolts do not work as well. Additionally, such a bolt must provide a fluid seal between it and the skull and a fluid seal between it and the inserted instrument or instruments as well as be easy to manipulate.
As used herein, an "instrument" includes a sensing catheter, drainage catheter, or other device designed for introduction into a biological location.
Additionally, a fluid seal for forming a sterile connection with the inserted instrument should be located as close to the patient's skull as possible to lessen the risk of infection.
Hence, those skilled in the art have recognized the need for a parenchymal bolt that not only secures an instrument in a desired position in relation to the ventricle of a patient, but that also reduces the risk of infection to the patient, is easy to install, permits rapid removal of the instrument, and that works efficiently for a wide variety of skulls. A device that is simple and inexpensive in construction, is easy to use, and is useable in a wide variety of conditions is also the subject of a recognized need. The present invention fulfills these needs and others.